I believe that the problem is at network manager and/or modem manager because when running (nm+mm or nm stopped mm running), after ejecting the initially created CD-ROM (sr0) some  seconds later (when it re-appears) the system partially freezes:

new terminal window opens but you cannot type anything
existed terminal windows are frozen totaly (you cannot close them except 'force close')
CTRL+ALT+F2  don't work
Shut down or reboot NEVER finalize, I need to press power button continuesly to do a 'hard' power off

After booting again (without the modem) terminal has already lost its history (up arrow)

modem: ZTE MF636 (Greece ?)
pc: EeePC 1000H
os: Linux KKa4 2.6.31-020631rc7-generic #020631rc7 SMP Sat Aug 22 09:51:01 UTC 2009 i686 GNU/Linux
nm: 0.8~a~git.20090820t182117.cb60390-0ubuntu2
mm:  0.2.git.20090821t194148.180ad40-0ubuntu2~nmt1
above  versions are from 'trunk', listed with: 'sudo aptitude show package-name'
tested also with 'typical alpha4' versions

Below is the SUCCESSFUL connection method:
**********
g@KKa4:~$ sudo /etc/init.d/NetworkManager stop
[sudo] password for g: 
 * Stopping network connection manager NetworkManager                    [ OK ] 
g@KKa4:~$ ps -A | grep modem
 2508 ?        00:00:00 modem-manager
g@KKa4:~$ sudo kill 2508
g@KKa4:~$ ps -A | grep modem
g@KKa4:~$ # ------> MODEM ATTACHED NOW, WAIT 20sec
g@KKa4:~$ dmesg | grep CD-ROM
[  150.920937] scsi 2:0:0:0: CD-ROM            ZTE      USB SCSI CD-ROM  2.31 PQ: 0 ANSI: 2
[  150.948117] Uniform CD-ROM driver Revision: 3.20
[  150.949905] sr 2:0:0:0: Attached scsi CD-ROM sr0
g@KKa4:~$ sudo eject sr0
g@KKa4:~$ # -------> WAIT 10sec
g@KKa4:~$ lsusb | grep 19d2
Bus 001 Device 004: ID 19d2:0031 ONDA Communication S.p.A. 
g@KKa4:~$ dmesg | grep ttyU
[  183.957799] usb 1-2: GSM modem (1-port) converter now attached to ttyUSB0
[  183.958218] usb 1-2: GSM modem (1-port) converter now attached to ttyUSB1
[  183.958681] usb 1-2: GSM modem (1-port) converter now attached to ttyUSB2
g@KKa4:~$ pppd ttyUSB2 nodetach defaultroute noipdefault lock usepeerdns connect 'chat "" "at" "" "at" "OK" "at&f" "OK" "atz" "OK" "at+cgdcont=1,'IP','gint.b-online.gr'" OK "atdt*99***1#" CONNECT' user web password web
Serial connection established.
Using interface ppp0
Connect: ppp0 <--> /dev/ttyUSB2
CHAP authentication succeeded
CHAP authentication succeeded
Could not determine remote IP address: defaulting to 10.64.64.64
Cannot determine ethernet address for proxy ARP
local  IP address 212.152.103.76
remote IP address 10.64.64.64
primary   DNS address 212.152.70.6
secondary DNS address 212.152.70.7
**********

Actions done:
0. boot without modem, wait for the system to fully load
1. STOP network manager
2. KILL modem manager
3. modem attached
4. ZeroCD ejected
5. check: 'real modem state' (lsusb), ttyUSBx creation (dmesg)
6. connected via pppd command (chat included)
7. all terminal copied and pasted here (using above connection)

Additionally I attach the 'problematic' dmesg (MF636_onlyMM_dmesg.txt).
In that test, nm was stopped, mm killed, mm started as --debug, modem attached. Copied from terminal using mouse. Keyboard was not functional via terminal window.

In next post I will send the 'debug' output from modem-manager (MF636_onlyMM_debug.txt)

Final note: when both run (network-manager & modem-manager) it is very hard to get data because of partially --> total stuck of the system.

Regards,
George